The present invention is directed to glycosulfopeptides, methods of their synthesis, and methods of their use in treating inflammation.
Inflammation is the reaction of vascularized tissue to local injury. This injury can have a variety of causes, including infections and direct physical injury. The inflammatory response can be considered beneficial, since without it, infections would go unchecked, wounds would never heal, and tissues and organs could be permanently damaged and death may ensue. However, the inflammatory response is also potentially harmful. Inflammation can generate pathology associated with rheumatoid arthritis, myocardial infarction, ischemic reperfusion injury, hypersensitivity reactions, and some types of fatal renal disease. The widespread problem of inflammatory diseases has fostered the development of many “anti-inflammatory” drugs. The ideal drug would be one that enhances the good effects resulting from the inflammatory response, and at the same time prevents the potentially harmful side-effects of this response.
The inflammatory response in regard to blood cells is accompanied by adhesion of circulating neutrophils, the most abundant phagocytic cell in the blood, to activated endothelial cells that line the vessels and make up the vessel walls. The adherent neutrophils are subsequently activated and the activated neutrophils emigrate from the blood into the surrounding tissue in a process termed diapedesis. The cells then begin engulfing microorganisms in a process termed phagocytosis and they also degranulate, releasing a variety of degradative enzymes, including proteolytic and oxidative enzymes into the surrounding extracellular environment. The mechanisms by which neutrophils adhere, become activated, and emigrate from the blood are currently major topics of research around the world. It is hoped that a fundamental understanding of these mechanisms will give rise to a new generation of anti- and pro-inflammatory drugs and treatments.
The initial attraction of circulating leukocytes to sites of inflammation is due to binding of the cells to a class of adhesion molecules termed selectins. The three currently identified selectins are L-selectin, which is constitutively expressed on the surfaces of all circulating leukocytes; E-selectin which is inducibly expressed on the surfaces of endothelial cells; and P-selectin, which is inducibly expressed on the surfaces of platelets and endothelial cells. The selectins recognize counter-receptors on other cells and thereby mediate cell-to-cell adhesive contacts. For example, P-selectin binds to a constitutively expressed, mucin-like glycoprotein counter-receptor on neutrophils termed the P-selectin glycoprotein ligand-1 (PSGL-1). the interaction between P-selectin and PSGL-1 promotes tethering and rolling adhesion of neutrophils on the vessel wall leading to neutrophil activation and eventual tight adhesion and diapedesis via integrins and their counter-receptors. Since it is well established that the selectin-mediated adhesion is an essential prelude to neutrophil activation and emigration during the inflammatory response, a tremendous amount of research has been done to identify compounds that inhibit neutrophil adhesion.
There have been attempts to use sialyl Lewisx mimetics to control or regulate the inflammatory response via inhibition of selectin-mediated adhesion [Lowe, “Therapeutic Inhibition of Carbohydrate-protein Interactions In Vivo,” J. Clin. Invest., 100(11 Suppl):S47–51, 1997]. These are modified simple carbohydrates (<2,000 daltons) that contain the sialyl Lewisx or sialyl Lewisa antigen [Varki, “Sialic Acids As Ligands In Recognition Phenomena,” FASEB Journal, 11(4):248–55, 1997]. The sialyl Lewisx mimetics have been made as either free carbohydrates or as adduct between the carbohydrates and lipids to alter their solubility properties. Synthesis of these mimetics has been by one of two routes. In one common method the carbohydrate mimetics have been produced by entirely chemical steps beginning with commonly available precursors and organic chemical approaches. In the other common method the carbohydrate portions of the sialyl Lewisx mimetics have been synthesized primarily using recombinant or partly purified glycosyltransferases, including sialyltransferases, galactosyltransferases, fucosyltransferases and sugar nucleotide donors, such as cytosinemonophosphate sialic acid, uridinediphospho galactose and guanosinediphospho fucose. In all cases, the efficacy of these sialyl Lewisx mimetics has been poor and high doses (>0.5 mM) of the compounds are required, because they do not accurately reflect the structure of the appropriate selectin counter-receptor, e.g., PSGL-1, for P-selectin.
PSGL-1 on human leukocytes contains at its extreme amino terminus tyrosine residues that can potentially be sulfated and threonine residues that are potential binding sites for attachment of O-glycans containing N-acetylgalactosamine, N-acetylglucosamine, galactose, fucose and sialic acid with the sequence of the sialyl Lewis x antigen (McEver et al., “Leukocyte Trafficking Mediated by Selectin-Carbohydrate Interaction”, J. of Biol. Chem., 270:11025–8, 1995. McEver et al. , “Role of PSGL-1 Binding to Selectins in Leukocyte Recruitment”, J. of Clin. Invest., 100:485–491, 1997).
The co-expression of sulfated tyrosine residues and the O-glycan appears to be required for high affinity interactions between PSGL-1 and P-selectin. However, naturally-occurring quantities of PSGL-1 are limited and it is not feasible to produce PSGL-1 from human neutrophils in a form suitable for administration as an anti-inflammatory compound. Moreover, recombinant means of synthesis of PSGL-1 are tedious and expensive and require animal cell culture and the consequent problems and uncertainties of proper post-translational modifications of the PSGL-1 peptide backbone, of which tyrosine sulfate and O-glycan addition are examples. It would be desirable to have a process which enables the formulation and production of compounds which overcome these problems.